1. Technical Field of the Invention
This invention most generally relates to the alignment of planar arrays of electro-optical devices with optical link connectors used for multi-channel optical data communications; and more particularly to a method for mapping the results of the physical alignment of an optical array to a multi-channel optical link connector where multiple electro-optical devices are available for each optical channel to optimize an emitter/detector pair and provide redundancy.
2. Background Art
Integrated circuit technology allows large numbers of VCSEL (Vertical Cavity Surface Emitting Laser) laser emitter optical transmitters and p-i-n diode photo detector optical receivers to be constructed as large, two dimensional planar arrays, with one or more such arrays mounted on a common ASIC (Application Specific Integrated Circuit) substrate, as by flip-chip methods, also known as hybridization mounting techniques, each emitter and/or detector of the array making electrical connections with circuitry previously constructed in the ASIC substrate. This compound device, when coupled with precision alignment to a terminal end or node of a multi-channel optical link such as the end of a fiber optic bundle, provides an electro/optical communications interface where an electronic signal is converted by a VCSEL to an optical signal, directed at a end face of a single channel optical core of a terminator/connector, and hence along an optical transmission path fiber within the bundle, to be discharged via a carefully aligned receiving end fiber terminator/connector into a photo diode opto-electronic receiver on the same or another optical array of the same or another ASIC substrate, and converted by that photo detector back into an electronic signal. Fiberoptic communications channels provide significantly greater speed and effective bandwidth capabilities as compared to electrically conductive leads.
Each core end of the optical fiber bundle terminator or connector must be carefully aligned with its VCSEL on one end and corresponding detector on the end in order for the optical communications channel to be effective. Light pipes and image guides are commonly used to terminate a fiber bundle and connect the individual light fibers to their respective optical elements in planar photo arrays. These must be carefully aligned without actual contact and mechanically fastened to the planar array or its ASIC substrate so as to maintain optical alignment. Sufficient misalignment between the optical face of the array and the terminator face, in any of the Z-axis parameters of lateral offset, rotation, tilt, and spacing as between a multi-channel fiber terminator and a photo optic array, can cause a significant number of optical channels to be unusable.
As the density of the arrays of emitters and detectors increases, coupling a multi-channel fiber optic cable, image guide, or other optical connector or terminating device to the transceiver array becomes an increasingly more arduous task. Lateral offset and rotation alignment are particularly burdensome, while spacing and tilt alignment are more easily controlled with proper mechanical connectors and spacing structures.
What is needed is a device and system for self alignment of emitters and detectors that can determine the optimal emitter/detector pair as well as establish spare detectors and emitters that can be used when the primary emitter/detector pair degrades in performance. Such an invention should allow multiplexing of emitters operating at a single wavelength to be transmitted in a single fiber and be demultiplexed at the other end by the detectors. There can be a memory section that stores the insertion loss values of the mapping process to enable redundant emitters and detectors to quickly switch over form faulty emitters or detectors.
The invention is devised in the light of the problems of the prior art described herein. Accordingly it is a general object of the present invention to provide a novel and useful apparatus and technique that can solve the problems described herein.
It is an objective of the invention to provide a method for determining the alignment of a multi-channel optical link connector to a planar optical array.
It is another objective of the invention to provide a method for determining the alignment of each of the channels of a multi-channel optical link connector to the optical devices on a planar optical array.
It is a further objective to provide a method for determining the alignment of both ends of each of the channels of a multi-channel optical link to the optical devices of respective planar optical arrays.
An object of the invention is a self-aligning apparatus for electro-optical devices and optical connectors, comprising at least one planar array containing a plurality of optical detectors and a plurality of optical emitters with respective drive circuitry for said emitters and said detectors. There is at least one optical link connecting the emitters and the detectors of the planar array, wherein the optical link establishes an illumination area within the plurality of detectors. A processing section is coupled to the detectors and coupled to the emitters, wherein the processing section controls light signals from the emitters to the illumination area and wherein the processing section performs selective measurements of the light signals with the detectors, and wherein the processing section selects a primary emmiter/detector pair based on the measurements.
Another object is the self-aligning apparatus, wherein based on the measurements the plurality of optical detectors comprise one or more spare detectors that are switchably connectable, or one or more spare emitters that are switchably connectable.
An additional object is the self-aligning apparatus, further comprising a monitoring section coupled to the primary emitter/detector pair to monitor performance of the primary emmitter/detector pair. Based on said measurements, one or more spare emitter/detector pairs can be substituted for the primary emitter/detector pair.
And a further object is the self-aligning apparatus, wherein the optical links are optical couplers selected from the group comprising ordered fiber bundle, image guide, waveguide, pigtail and microlenses. In addition, the optical links can be transmissive mediums selected from the group comprising free space optics and guided wave optics.
In one embodiment of the self-aligning apparatus, the processing section cycles through the detectors one at a time with one or more emitters active to precisely locate the illumination area. The cycling establishes a mapping of the measured values. Therefore, the device can include a memory section, wherein a table of insertion loss values from the selective measurements are stored in the memory section.
An additional object is the self-aligning apparatus, wherein the emitters and the detectors are located on separate planar arrays. The emitters can be located on different planar arrays and can even be separated from each other, as the present system performs a multiplexing/demultiplexing function.
Yet a further object is the self-aligning apparatus, wherein the emitters function as detectors by changing a voltage polarity of the emitters.
It should be apparent to those skilled in the art that the optical detector is a device that converts energy of incident radiation into electrical energy. There are various types of such devices and the present invention is not limited to a specific device. Likewise, the emitter is a device that emits radiation when electrical energy is applied, and is not specific to any one device.
An optical communications device with built-in redundancy, comprising at least one array containing a plurality of optical detectors and at least one array containing a plurality of optical emitters with respective drive circuitry for the emitters and detectors, wherein a group of emitters form an emitter channel and a group of detectors form a detector channel and the group of said emitters and the group of detectors operate at a single wavelength. There is at least one emitter multiplexer coupled to the emitter channel, and at least one detector demultiplexer coupled to the detector channel. There are one or more optical links connecting from the emitter multiplexer to the detector demultiplexer. A processing section is coupled to the detectors and coupled to the emitters, wherein the processing section controls light signals from each of the emitters of the emitter channel to each of the detectors in the detector channel and wherein the processing section performs selective measurements to establish a redundancy hierarchy. The redundant hierarchy can be a table of emitter and detector pairs based on criteria such as insertion loss.
In contrast to the many applications attempting to utilize different wavelengths, the present invention has found that using a single wavelength as described herein provides some significant benefits to the present device.
A further object includes the multiplexing/demultiplexing device, wherein the plurality of optical detectors comprise redundant detectors and emitters that are switchably connectable.
And another object is the multiplexing/demultiplexing device, wherein the optical links are selected from the group comprising ordered fiber bundle, image guide, waveguide, pigtail, and microlenses. The light from disparate emitters can be muxed onto a single optical fiber and demultiplexed by the detectors utilizing the teachings of the present invention.
An additional object is the multiplexing/demultiplexing device, wherein the processing section cycles through the detectors one at a time for a single emitter to establish the channel. Alternatively, all the emitters can be cycled for an individual detector.
For proper performance of electro-optical planar array devices used to provide data communications over optical links, it is essential that there is sufficient control over the alignment of the optical array face with respect to the optical link connector to assure an effective optical communications channel is present between identifiable sets of emitters and detectors. This invention desensitizes the precision required of the physical alignment of a multi-channel fiber optic link connector to the optical planar array face as compared to the one to one correspondence between an optical fiber termination and an optical device as used in the prior art.
The invention depends on using undersampling techniques that assume each fiber will be optically connected to several emitters on one end and/or several detectors on the other end, in combination with an automated mapping of the physical alignment of a non-precision connection which sorts out the available channels of the optical link and the emitter sets and detector sets common to each channel. This self-determination methodology of alignment provides data that then permits selection and de-selection from among the individual emitters and detectors on each array in accordance with various schemes for optimizing the performance of each channel of the communications link.
VCSELs can be produced in planar arrays by several methods. Ion-implanted VCSELs can be made with a diameter ranging from 20 to 100 microns. Oxide VCSELs can range from 20 to 60 microns. Etched-post VSCEL arrays are now feasible with VCSEL diameters of 5 to 40 microns; and with a 2 micron wide trench, can have a pitch as small as about 7 microns. This provides the potential for a significant planar face density of optical devices per fiber channel, using, for example, 50 or 62.5 micron diameter fiber cores terminated in a suitable connector.
There are several intuitive methods for aligning an optical fiber array to its respective electro-optical array to achieve accurate device-to-channel alignment according to the present invention. The fabricator may simply observe the electro-optical devices through a part of the connector and visually or xe2x80x9cpassivelyxe2x80x9d align target reference points of the components, perhaps with the aid of a transparent fiber alignment faceplate or template. Another method is to interconnect all of the various electrical and optical assemblies and perform xe2x80x9cactivexe2x80x9d final physical alignment of the multi-channel fiber connector to the optical array so as to optimize the multi-channel connection as seen at the detector side of the optical link, and then secure the connector to the optical array or its ASIC substrate in that precise position. In either event, each such connection requires a closely controlled, precise step in the assembly process that contributes to the time and cost to assemble devices employing this technology.
Summarizing one technique of the invention for the simpler case, during the self-alignment of an under-sampled transmitter array to the fiber bundle, the transmitters devices are activated, for example in a rastering mode, while the detector array receiving the time-related impulses, and its controlling software embedded in the underlying ASIC or in the ASIC in combination with remote circuitry and software, map the unique set of adjacent transmitters producing a respond in each detector. If the detector array is connected on a one to one basis with the fibers or optical channels of the optical link, then the emitter set for that channel has been identified, in effect establishing the result of the physical alignment and mounting of the fiber optic connector to the transmitter array.
The use of multiple emitters per channel, along with the self-determined alignment information, provides further opportunities for individual selection, de-selection and control of the emitters within the set to optimize the use of each channel. As will be readily apparent to those skilled in the art, the corresponding methodology and the further opportunity for the case of an under-sampled receiver array is quite similar, except that detector sets for each emitter channel are identified, and subsequent control of detectors can be exercised for optimizing channel performance.
In the simplest case, for determining which detectors have been excluded from all possible channels by the particular physical connection of a multi-channel optical link to a detector array, as made during fabrication, the all-channels to all detectors alignment can be accomplished by simply illuminating the other, input end of the optical link with an expanded beam of suitable wavelength so that detectors adequately coupled to any channel that will respond and be recognized.
A logical further scenario is where there are multiple optical devices at each end of each fiber channel. They may, of course, be on the same optical chip, on different optical chips on the same ASIC substrate, or on optical chips on different ASIC substrates. The invention also extends to chips of any sort that may integrate the ASIC and electro-optical surface arrays for both intra-chip and inter-chip optical communication, where assembly requires physical alignment of a multi-channel optical link connector to at least one planar array of optical devices on the chip, or as in this case, with both ends of the multi-channel link connected each to a planar array of optical devices.
In this case, the automatic self-determination alignment methodology of the invention requires the following steps:
1. Interconnect two planar arrays of very small electro-optical devices of photo-emmitters and detectors with a multi-channel fiberoptic bundle, or optical link, where each end of the bundle is terminated by a suitable connector, each of which is attached to one of the arrays, so that each fiber of the bundle is linked to or xe2x80x9cseesxe2x80x9d at one end several electro-optical emitters on one array and is linked to or xe2x80x9cseesxe2x80x9d at its other end several electro-optical detectors on the other array. The interconnect step in this case is a relatively non-precise physical operation with respect to lateral offset and rotation, but is still sufficiently precise to assure proper Z-axis spacing and tilt tolerances of the optical link connectors to the optical arrays. It does not depend on critical alignment of channels to respective optical devices, but rather on overall array to connector edge alignment, since it is not necessary to establish an exact alignment or to achieve a pre-determined optical device-to-channel alignment at this stage.
2. Enable all of the detectors on the receiver array, or on both arrays, or each array in turn if using transceiver arrays. This is done through ASIC or ASIC in combination with remote control circuitry and software.
3. Raster or otherwise sequence the individual photo emitters of the transmitter array, both transmitter and receiver arrays, or each array in turn, if using transceiver arrays. This is likewise done through ASIC or ASIC in combination with remote control circuitry and software.
4. Record the particular detectors illuminated with respect to each emitter in turn. When an emitter device of the transmitting array is on, only those detectors that are aligned with the same optical fiber serving that emitter will have useful sensitivity. Blanket illumination of the detector arrays is prevented because of the occulting portions of the optical fiber array. The effect is the same for an ordered fiber bundle or a more common over-sampling image guide. The ability to monitor and record or xe2x80x9cmapxe2x80x9d the detector response is resident within the local ASIC, or is shared with remote control circuitry and software.
5. Establish, again through the ASIC or in combination with remote control circuitry and software, the detector sets of adjacent detectors common to each emitter as seen through the optical link.
6. Match up common sets of detectors to identify emitter sets of adjacent emitters using a common optical channel, again through the ASIC or in combination with remote control circuitry and software.
The methodology may be extended to mapping and recording the intensity or signal strength of each emitter/detector pair within a given optical channel, so that there may be a suitable initial selection from among the emitters and detectors of associated emitter and detector sets using the same channel that optimizes that channel of the communication link. The channel""s emitter/detector pairs intensity map can be periodically compared to a fresh mapping of channel intensity, for possible re-selection of suitable emitters and detectors from amount those available.
A table of insertion loss measurements can be used select the optimal emitter/detector pair. The table can be stored in memory so that as the emmiter/detector pair performance drops, the next best emitter/detector pair can be selected. This built in redundancy would be invisible to the user as the switch would occur through the drive circuitry. Alternatively, the whole mapping process could be repeated to establish a new table of insertion loss values for the emitter/detector pairs. Monitoring devices are known in the art and can evaluate the performance of the emmiter/detector pair for degradation. Alternatively, a simple timing schedule can be used to switch to a fresh emitter/detector pair after a certain time interval has elapsed. In another embodiment, the device could regularly switch between various emitter/detector pairs with satisfactory performance thereby prolonging the lifespan of all the emitter/detector pairs in the channel.
A further benefit of the undersampling and mapping scheme is that spare emitters and detectors within the channel are available, should there be a failure of one of these optical devices. The methodology supports the implementation of differential optical signals in a given channel, using selective combinations of available emitters and detectors from among the emitter and detector sets of the channel.
Elaborating on the concept of having spare emitters and detectors, the present invention provides for redundancy in the event of failure of the primary emitter or detector. Emitters and detectors do have a certain life span, and the spare device can remain inactive until a complete failure or a threshold failure of the primary device and then activated to become the primary device. Alternatively, there may be advantages to cycling between the primary devices and the spare devices to extend the life span of operation. The processing section can retain a log of operating periods and increase the test cycle of those devices nearing the end of the life span or otherwise transition to the spare device at a fixed time period.
In operation, the system performs measurements as part of the alignment process and the measurements are used to also track emitter and detector performance. An emitter failure within a group of emitters would easily be detected and by the measurement values. The spare emitter could then be switched into operation in place of the malfunctioning emitter. As the drive circuitry and processing section are integrally connected with the emitters/detectors, the transfer is seamless. Testing of receivers/detectors are accomplished in a similar manner by making measurements and when the measurements are no longer correct, the spare detector can be switched into the array. Discerning between emitter and detector errors can also be quickly ascertained by switching emitters and/or detectors.
On a larger scale, the methodology of the invention provides for periodic or automatic alignment assessments of the connector to the optical planar array to guard against creeping physical re-alignment due to environmental effects such as deforming temperature, torque or pressure on the device. When necessary, the fill, self-alignment mapping procedure can be run again to reset the baseline emitter and detector sets for each channel.
It will be readily apparent that fiber channels with multiple optical devices at each end, such as where being connected to transceiver arrays with uniformly distributed emitters and detectors, may have bi-directional capability for all or some channels. The fully defined physical alignment map provides the data necessary for selection, de-selection and control of the devices at each end of the link, enabling ASIC and remote control circuitry and software to manipulate both direction and performance of each channel, within the total capability of the devices associated with that channel.
It will be further apparent to those skilled in the art that the methodology can be extended to compound optical links having more than two connectors or nodes, where transmitters from one array may be linked with and communicating to detectors of two or more other arrays, or where detectors in one array may be linked to receive data from either of two or more transmitter arrays, or as may otherwise be required in variations of simplex, duplex, star and ring interconnect topologies.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein we have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by us on carrying out our invention.